(1) Field of the Invention
This invention relates to a complete system, in its broader aspects, for the printing of relatively small flat objects, e.g. piece parts such as compact discs. The system comprises means for sending the small flat objects from a stack thereof to a means for loading the small flat objects onto transport apparatus, means for loading the small flat objects onto transport apparatus, transport apparatus traveling in an oblong-shaped path to move the objects to one or more printing stations, one or more means mounted so as to face outwardly for the printing of the top surface of the objects with information or a decoration, after which the printed small flat objects are eventually transported to an off-loading station where the objects are off-loaded from the transport apparatus, means for off-loading the objects from the transport apparatus and means for receiving the small flat objects and providing them in a vertically disposed stack. In particular, the invention comprises a method of, and means for, loading and off-loading small flat objects onto and from transport apparatus, means for, and method of, delivering vacuum from a fixed vacuum source to a moving vacuum manifold provided on, and moving in unison with, transport apparatus, and printing apparatus mounted in combination with the transport apparatus for the printing of continuously moving small flat objects. More particularly, the invention relates to means for transferring vacuum from a stationary source to tooling mounted around the perimeter of a transport member or conveyor traveling in an oblong or oval-shaped path. Further, the invention relates, in the more preferred aspects, to flexographic printing means for the multicolor printing of a compact disc, and to means for the lateral and radial adjustment of the flexographic printing roll to print an image on a compact disc. The invention further comprises means for, and method of, determining the variations in height of compact disc tooling fixtures provided on a transport member for compact discs to be printed, as well as the differences in thickness of the compact discs being printed, and to adjust the height of the print roll for the changes in printed surface height.
(2) Background
U.S. Pat. No. 5,165,340 discloses a system for the multicolor printing of a compact disc. This system comprises, in its basic aspects, loading and unloading apparatus, an annular-shaped transport member for compact discs, means in combination with the loading and unloading apparatus supplying the compact discs to the loading apparatus in a vertically disposed stack of compact discs, means in combination with the off-loading apparatus for providing the off-loaded compact discs in a stack of compact discs, and silk-screen printing apparatus in operative combination with the annular-shaped transport member for the multicolor printing of the top surface of the compact discs. On the top surface of the transport member there are provided a plurality of spaced-apart compact disc fixtures, sometimes called tooling fixtures. These fixtures are each provided with a circular-shaped well for holding a compact disc while being transported.
In the silk-screen printing of the top surface of a compact disc, as disclosed in the aforementioned patent, the compact discs are each indexed, in turn, to one or more printing stations whereat a desired decoration is applied to the compact disc surface. Thus, an additional layer of decoration is applied to the compact disc surface at each of the printing stations. The registration of the successive layers of color applied is, in general, limited to the ability of the transport member to stop at repeatable locations. Moreover, in order to apply a decoration to the surface of a compact disc by a silk-screen printer, the transport member must be stopped momentarily. This, of course, limits the number of compact discs that can be printed over any given period of time. The problem is magnified, the more layers of decoration that must be applied to the surface of a compact disc and the more tooling fixtures provided on the transport member.
It is common, as disclosed in U.S. Pat. No. 5,165,340, to provide vacuum to each of the tooling fixtures individually so that, once a compact disc is registered for printing in a precise location in the well of the compact disc fixture, the compact disc will stay in that precise location from the time it is loaded onto the transport member until it is off-loaded from the transport member. The vacuum, as disclosed in that patent, is supplied to each of the plurality of tooling fixtures provided on the transport member independently, as and when desired, from a fixed source of vacuum to a vacuum manifold, hence to each of the tooling fixtures.
Although the means for (method of) transferring vacuum independently to each of the compact disc tooling fixtures, as disclosed in U.S. Pat. No. 5,165,340, is quite satisfactory, at least for some applications, nevertheless it has some limitations. The vacuum manifold in that vacuum system is of somewhat complex structure and operation For one thing, the vacuum manifold is defined by an annular-shaped groove located between two surfaces, one of which moves and the other of which is stationary. The stationary surface provides a top to the annular-shaped groove. The annular-shaped groove moves with the moving surface, i.e., the annular-shaped transport member, and is in sliding contact with the stationary surface, i.e., the support member for the silk-screen printing heads. In the stationary member there is provided a vertically disposed opening the upper end of which is connected to a fixed or stationary vacuum source. The annular-shaped groove is provided in opposition to the opening at its lower end. Thus, the surface of the manifold in sliding contact with the stationary surface on the fixed support member must be maintained in tight sealing engagement with that surface to prevent loss of vacuum to the tooling fixtures.
Another limitation with the vacuum system and manifold disclosed in U.S. Pat. No. 5,165,340 is that it is of annular or circular shape. This, in and of itself, presents no particular problem to the printing of the compact discs. The problem results from the fact that, because the compact disc transport member and print head support member are of annular or circular shape, the only way in which to provide for additional printing stations and curing ovens in such a system is to increase the diameter of the transport member and print head support member. This, of course, necessitates a larger diameter vacuum manifold. Such a larger diameter apparatus necessitates larger drive mechanisms due to higher inertial loads and, moreover, results in a higher number of printing errors because of the larger radius components involved. These increases in size of the silk-screen printing machine's components, moreover, require a considerable amount of additional floor space. Nevertheless, in some cases, it is impossible, or at least impractical, to increase the diameter of the transport member, etc., due to the lack of floor space that is available for expansion, or space that is of the right size and shape.
For the past several years, the printing of compact discs has been done by silk-screen printing processes and apparatus. Such a printing process is quite advantageous as a relatively thick layer of ink can be applied to the compact disc surface. Thus, it is possible to obtain good coverage and the result is a print image of good quality. The silk screen printing of compact discs is also advantageous because of the fact that it can compensate for the variations in thickness of the compact discs being printed due to the elasticity of the silk-screen. Nevertheless, silk-screen printing processes have their limitations. This manner of printing does not provide adequately for the reproduction of images having a high degree of detail and shades of coloring, i.e., halftone printing. Further, the registration of colors in the silk-screen printing of compact discs is best when only a few colors, e.g. four colors, are to be printed. Nevertheless, when a larger number of different colors are to be printed on the surface of a compact disc, as is now being done, and halftones, the registration of the colors shades of and color being silk-screen printed, one-to-the-other, becomes more difficult.
More recently, the printing of the top surface of a compact disc with multiple colors has been accomplished by use of not only silk-screen printing apparatus but also by offset printers in line with silk-screen printers. Such a combination is disclosed in U.S. Pat. No. 5,456,169. With offset printing one can obtain a print image with a high degree of fidelity and in a large number of colors and color shades, i.e., halftones. The use of a combination of printers, as disclosed in that patent, is apparently because of the fact that the amount of ink that can be put down on a surface by an offset printer is somewhat limited. Thus, the desired opacity of the ink placed on a substrate by offset printing may be lacking. Accordingly, a silk screen printer is used to put down a first layer of ink, e.g., a white background layer, to provide the desired opacity so that the color of the surface to be printed is hidden. Then, the surface is printed by an offset printer.
The combination of printers, as disclosed in U.S. Pat. No. 5,456,169, is undesirable, however, for a number of reasons. First of all, this combination of printers suffers from the same problem in using silk-screen printers alone, i.e., the transport member must be indexed to a silk-screen printing station, stopped, and then the compact disc is printed. Not only is the transport member in this combination indexed for the silk-screen printing of the compact discs, it is also indexed to an offset printing station, stopped, and then the compact disc is printed. Moreover, the use of offset printers for the printing of compact discs presents its own problems.
In the offset printing process disclosed in U.S. Pat. No. 5,456,169, each of four partial print images is transferred by a plate cylinder in usual manner to a generally continually rotating printing or blanket cylinder. The four partial images go together to form an overall print image. This overall print image is then transferred onto the compact disc surface. This presents a problem, however, in the registration of one color/partial image to the next as the colors are each first printed, in turn, onto a transfer blanket, wet ink upon wet ink, and then transferred from that blanket as a single image to the compact disc surface. The printing of wet ink upon wet ink disadvantageously results in bleeding from wet ink to wet ink and changes in color tones.
The transfer blanket or means on the blanket cylinder does not extend over the entire periphery of the cylinder and comprises a plurality of transfer means, each two of which is divided by a space. Thus, the blanket cylinder has two different radii, one for the surface of the transfer blanket means and another for the empty space between. Thus, there is only intermittent contact by the printing cylinder with the plane of the surface of the article to be printed Therefore the printing cylinder can continuously rotate without need for the printing cylinder to be raised following the printing of a compact disc. This is believed of little advantage, however, as the transport member disclosed is an indexing one and printing only occurs when the compact disc is stationary.
As disclosed in U.S. Pat. No. 5,456,169, there is a need to take into consideration in the offset printing process not only the variations in thickness of the compact discs, but also the need to consider variations in thickness and configuration of the printing blanket or transfer means on the printing cylinder. Thus, prior to being offset printed a the position, i.e., the level of the surface of the compact disc, is determined by a sensor, and the sensor's output sent to a computer and stored therein, later to be called out. A sensor device is also associated with the surface of the transfer blanket portions on the printing cylinder whereby the positions of those surfaces can be determined and an output signal sent to the computing arrangement and stored. These two components determine the height at which the offset printing arrangement, i.e., the printing cylinder mounted thereto, should be during the printing operation relative to the surface to be printed and whether the printing arrangement should be adjusted upwardly or downwardly from a previously determined base plane, to produce the best pressure effect of the transfer surface against the surface to be printed. Thus, signals are sent from the computer arrangement disclosed to an adjusting motor whereby the frame of the printing arrangement is caused to be raised or lowered relative to the surface of the compact disc to be printed. The adjusting motor operates to cause a slide member having two inclined surfaces in contact with two rollers associated with the frame to move in a back and forth direction depending upon the height adjustment to be made. Although, this method for the adjustment of the printing cylinder relative to the plane of the surface to be printed would appear to provide satisfactory results, the apparatus for accomplishing such seems overly complex.
U.S. Pat. No. 5,456,169 also discloses means upstream of the offset printing station for detecting whether there is a compact disc present on the holder therefor to be printed. That signal is sent to the computer and later called out to provide a web of paper on which the image can be printed that should have been printed on the missing compact disc. The reason for this is so that the print plates will not print a second image upon the one still remaining on the transfer blanket
Of further concern with the offset printing apparatus and process disclosed in the above-mentioned patent, is the fact that offset printing does not perform well in combination with an annular-shaped transport member, such as disclosed in U.S. Pat. No. 5,165,340, or other transport members that travel in a circular defined path of travel, as disclosed in U.S. Pat. No. 5,456,169. Such a printer performs best when it is located in a straight line path of travel, like in the printing of newspapers. Thus, the offset printer in the latter patent is located in relation to the circular-shaped transport apparatus so that the printing cylinder can be moved laterally during the printing operation, i.e., in a direction perpendicular to that taken by the doctor blade during the silk-screen printing operation.
Accordingly, there is believed a real need for a printing system for piece parts, e.g., compact discs, that does not involve an indexing transport member. Further, there is need for a printing system that is capable of printing a compact disc surface while the compact disc is in continuous motion whereby a larger number of compact discs can be printed over a given period of time. There is also a need for a printing system that is capable of printing the surface of a compact disc without need for first printing the compact disc by silk-screen printing means to provide a layer of ink that provides good opacity. Also there is need for a printing system capable of printing a multiplicity of colors and halftones on the surface of a compact disc with precise registration of the different colors and shades of color being printed. There is also a need for a method of, and means for, transferring vacuum from a fixed source of vacuum to a vacuum manifold moving in conjunction with transport apparatus independently to at least one of a plurality of tooling fixtures provided on the transport apparatus, when and as desired. Further, there is a need for a better method of, and apparatus for, adjusting for the variations in thickness in compact discs to be printed, in a printing run, and for adjusting to variations in the height of the compact disc tooling fixtures.
Flexographic printing, i.e., direct rotary printing, has heretofore long been used; however, that use has been primarily in the printing of web press or corrugated carton technology. In such an application, the substrate to be printed is passed between the impression plate, which is mounted on the impression roll and the pinch roll. The gap between the impression roll and pinch roll in such an application, is adjustable to account for the thickness of the substrate that is being passed between these two rolls. Moreover, the impression roll and pinch roll are geared together to assure that the substrate being printed passes between the two rolls at a constant speed. Flexographic printing has, until the recent past, been used to deposit print in low definition applications such as earlier named. Recently, however, due to quality control in inks and anilox rolls, as well as advances in the technology used to manufacture the print plates, higher definition printing has become possible.
In flexographic printing, a thicker layer of ink can be put down on a surface than in the case of offset printing. Thus, flexographic printing offers the advantage that a layer of ink or decoration put down on a substrate provides better opacity than does offset printing. Flexographic printing offers the advantage also of a direct rotary printing process and apparatus of somewhat simpler construction than found with offset printers. Further flexographic printing is a continuous process and printing is done on the fly so-to-speak.
Thus, it would be quite advantageous if flexographic printing technology could be adapted to the printing of piece parts, e.g., compact discs. To do so, however, requires a considerable number of changes to be made to the design of conventional flexographic printing apparatus. In the printing of compact discs, the pinch roll in the flexographic printing apparatus needs to be removed. And, the tooling fixture for the piece part needs to be substituted for, and take the place of the pinch roll. The nip in this case is between the printing or impression plate and the top surface of the compact disc tooling fixture. Accordingly, it is of utmost importance that the nip between the tooling fixture top surface (and piece part surface to be printed) and the impression plate or roll has a precise and repeatable height, as would be the nip between the pinch roll and impression roll in printing web stock. This is made somewhat difficult, however, due to the fact that the tooling fixtures do not, in and of themselves, have top surfaces that are all of the same height from the top planar surface of the transport member. This results from the lack of reproducibility in the tolerances of the tooling fixtures one from another. In the printing of compact discs, this can be a real problem where the transport member may have a large number of tooling fixtures. At present time, a transport member may have as many as thirty-nine (39) or more tooling fixtures. And, in the future, it is likely that even a much larger number of tooling fixtures will be provided on a transport member. Further, the problem is somewhat compounded because the thickness of the compact discs may themselves vary due to differences in the molds for molding the compact discs, and other processing irregularities.
Another problem presented by removing the pinch roll and replacing it with a compact disc fixture, in the case of the flexographic printing of the surface of a compact disc, results from the fact that the means for ensuring that the compact disc passes through the nip formed by the print roll and tooling fixture at a constant speed is removed. The two are not geared together as are the print roll and pinch roll in conventional flexographic printing. Thus, the means for preventing slippage and for maintaining the compact disc at a constant speed while passing through the printing station is not present. Moreover, the lack of such a means to maintain constant speed effects the registration between the image on the print roll and the location on the compact disc surface where the image is to be printed.
A still further problem in the application of flexographic printing technology to the printing of compact discs results from the fact that the tooling fixture may not always have a compact disc thereon to be printed. This can come about because of several reasons known to those skilled in the art, e.g., a compact disc is not sent by the sender to the loading apparatus, or the loading apparatus does not, for some reason, load a compact disc into a tooling fixture. Even though no compact disc is present in the tooling fixture, the anilox roll nevertheless conventionally transfers ink to the printing plate on the print roll and another layer of ink is transferred to the printing plate after the anilox roll next passes through the ink source.
There is a need therefore, in the application of flexographic printing technology to the printing of compact discs, for means for determining that the nip between the top surface of a compact disc tooling fixture and the printing roll has a precise and repeatable height, as would the nip between the pinch roll and impression roll in printing web stock. There is also a need for means to determine, and to provide for, the differences in the heights of the compact disc tooling fixtures, and the compact discs themselves being printed in the flexographic printing of compact discs. Further, there is need for means in such a printing process to provide that a compact disc passes through the nip formed by the print roll and tooling fixture at a constant speed. And there is also a need to alert the printing roll in advance, that no compact disc is present in a tooling fixture to be printed.